Since the main translation thread is locked, I place this here:
I would like to work on a translation in my native language. But I have some tech uncertainties here.
I loaded the *.rc file into AP, and noticed a lot of ampersand characters in the file concerning the strings inside the "".
Sometimes as a leading character, sometimes in the middle of some string.
Sometimes logical, like '&File', but sometimes not, like 'Insert c&haracter'
How do I have to deal with it ? Keep implementing it, or ignore it, or what ?

I understand that. So in my case this would mean a conversion into "&Bestand".
But how about "c&haracter" for example. Should I edit this in my case as "k&arakter" ?
There must be some syntax about this.

While translating you can define your own accelerators. It does not match english in all the cases. If you can translate character as karakter you can put an & sign before a letter which you'd like to turn into an accelerator key. E.G. I was inspired by the other windows applications e.g. wordpad, notepad and all that common stuff where similar items can be seen.
I have even gone too far that I have added such a shortcuts to the settings dialog and to the various other controls where there are no underlined letters in the english version.

Ah, thanks, so it has to do with assigned shortcuts.
Still I don't understand quite well what's the link between the "i"' of 'Ctrl+I' and the position of the ampersand in 'Insert character'.
Is this what you mean with "It does not match english in all the cases." ?

Anyway, I can already start working now step by step with a renamed clone of the original file.

Still I don't understand quite well what's the link between the "i"' of 'Ctrl+I' and the position of the ampersand in 'Insert character'.

There is no connection. Ctrl+i is the shortcut key from the accelerators table. This can't be modified while translating user interface.
& sign is put in front of I so when that menu is displayed you don't need to use your mouse or press arrows to highlight the item you can just press i and the item will be activated. If you don't care about keyboard access you should even discard all such &.